Impedance transformer for vhf bands



June 10, 1969 MITSUO MATSUSHIMA ET AL 394493704 IMPEDANCE TRANSFORMER FOR VHF BANDS Filed March 16, 1967 V I Shet of4 Prior Ari INVENTORS Ml T500 MA TJUSl-l/MA TAD/ll/AAU A/(M/O 5///6/?U X4 70 June 10, 1969 rrsuo MATsUsHlMA ET AL 3,449,704

IMPEDANCE TRANSFORMER FOR VHF BANDS Filed March 16, 1967 Sheet 3 of 4 INVENTORS M/TSl/O MATSUS/l/MA 740A HA RU AK/NO June 10, 1969 rrsuo MATSUsHlMA ET AL 3,449,704

IMPEDANCE TRANSFORMER FOR VHF BANDS Filed March 16, 1967 FREQUENCY MQ/S) A m2 mmOJ ZOrEmmZ;

INVENTORS MITSl/O MATSUSH/MA TADAHARU AK/NO S/i/6fRU KATO United States Patent 3,449,704 IMPEDANCE TRANSFORMER FOR VHF BANDS Mitsuo Matsushima, Higashi Katsushika-gun, and Tadaharu Akino and-Shigeru Kato, Ichikawa-shi, Japan, assignors to TDK Electronics Company, Limited, Tokyo, Japan, a corporation of Japan Filed Mar. 16, 1967, Ser. No. 623,696 Int. Cl. H01f 17/06, 27/28 U.S. Cl. 336-175 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to the improvements of impedance transformers for VHF bands.

In the prior art, such an impedance transformer has twin-lead or bifiler windings on a coil bobbin or magnetic core and has a required connection. For example, an impedance transformer for the input circuits of a television receiver has a few turn windings of twin-lead 4 and 5 matched with the characteristic impedances of the circuits on a magnetic core 3 having two through holes 1 and 2 as illustrated in FIG. 1. It can be used for the impedance matching of two circuits of an impedance ratio of 4:1 between terminals 6 and 7, if necessary, either in a balanced to balanced connection as in (A) in FIG. 2 or in a balanced to unbalanced connection as in (B) in FIG. 2. By this transformer, the antenna circuit of an impedance of 3009 and an input circuit of a television receiver of 759 can be matched with each other.

However, in the conventional transformer, the characteristic impedances of the twin-leads, the dimensions of the magnetic cores and the permeabilities around the two through holes are so nonuniform that the characteristics will be nonuniform. In manufacturing such transformer, the operations of winding the twin-leads through the two holes and removing the film covering the twin-leads can not help being complicated. Further, as the magnetic core has two holes, it can not be made so small. Therefore, there are great defects that the characteristics are not uniform, that the price is not low and that the magnetic core can not be made smaller. The present invention has been suggested to eliminate the above mentioned defects.

An object of the present invention is to provide an impedance transformer wherein the characteristics are uniform, the operation of winding wires is simplified and the size can be easily made smaller.

Another object of .the present invention is to provide an impedance transformer wherein the impedances of two circuits can be matched by only limiting the shape dimension ratio and the frequency transmitting characteristics are improved.

An embodiment of the present invention shall be explained with reference to the accompanying drawings.

FIG. 1 illustrates a conventional impedance transformer.

(A) and (B) in FIG. 2 show a balanced to balanced connection diagram and balanced to unbalanced connection diagram of an impedance transformer, respectively.

FIG. 3 illustrates an impedance transformer of the present invention.

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(A) and (B) in FIG. 4 show connections of balanced to balanced and balanced to unbalanced impedance transformers, respectively.

FIG. 5 shows insertion loss characteristics of an impedance transformer of the present invention.

FIG. 6 shows SWR (standing wave ratio) characteristics.

FIG. 7 illustrates the details of an impedance transformer of the present invention. Therein, (A) is a wiring diagram, (B) is a vertically sectioned view and (C) is a cross-sectioned view.

FIG. 8 shows relations between the ratio of the outside diameter to the inside diameter of the magnetic core and the insertion loss in the impedance transformer.

FIG. 9 shows relations between the ratio of the length to the inside diameter of the magnetic core and the insertion loss in the impedance transformer.

FIG. 10 shows an example of application of an impedance transformer according to the present invention.

FIG. 3 illustrates an impedance transformer embodying the present invention. In the drawing, 8 is a magnetic core in which a primary winding 10 made, for example, of a polyurethane enameled copper wire is wound by two turns and a secondary winding 11 is wound by one turn through a through hole 9 and they are connected either in a balanced to balanced as in (A) in FIG. 4 or in a balanced to unbalanced as in (B) in FIG. 4, if necessary, so that the impedances of two circuits of an impedance ratio of 4:1 may be matched with each other between the terminals 12 and 13.

In the impedance transformer according to the present invention, in order to decrease the leakage inductance which will deteriorate the high frequency transmitting characteristics or will increase the insertion loss and to decrease the wiring volume, it is necessary to make the hole 9 made through the magnetic core as small as possible, to bring the wirings 10 and 11 into close contact with the inside wall of the magnetic core and to wind the primary winding on the magnetic core in turns spaced from each other as much as possible. In the thus formed impedance transformer, the characteristics are uniform, the winding operation can be simplified and the shape is so simple that the size can be easily made smaller.

FIGS. 5 and 6 show characteristics of a balanced to unbalanced impedance transformer made by winding 21 primary winding by two turns and a secondary Winding by one turn on a cylindrical Ni=Cu=Zn series ferrite magnetic core of an outside diameter of 5 mm., inside diameter of 1 mm. and length of 20 mm. FIG. 5 shows insertion losses, the frequency being taken on the abscissa and the insertion loss being taken on the ordinate. FIG. 6 shows VSWR, the frequency being taken on the abscissa and the VSWR (voltage standing wave ratio) being taken on the ordinate. It is found from this diagram that, in a frequency band of 20 to 250 mc./s., the insertion loss is less than 1 db and VSWR is less than 1.2. It is found from this fact that the same characteristics as of a conventional product can be obtained in the product of the present invention and that the product of the invention can be well practically used, for example, for matching impedances of the input circuits of a television receiver.

In the impedance transformer of the above mentioned formation, when a cylindrical high frequency magnetic body is made a magnetic core for the transformer, the primary and secondary windings are wound so as to be in very close contact with the inside wall of the magnetic core and the ratio of the outside diameter to the inside diameter and the ratio of the length to the inside diameter of the magnetic core are properly selected, the leakage inductance will be able to be made smaller and the high 3 frequency transmitting characteristics will be able to be improved.

In FIG. 7, (B) is a vertically sectioned view of an impedance transformer of the formation in (A) and (C) is a cross-sectioned view of the same. 14 and 15 are terminals on the primary side. 16 is center tap. 17 and 18 are terminals on the secondary side. 19 is a cylindrical magnetic core. 20 is a hole in the center of the magnetic core. D is the inside diameter of said cylindrical magnetic core. D is the outside diameter of the same. L is the length of the same. The inside diameter D of the cylindrical magnetic core is made as small as possible. The primary winding and the secondary winding are brought into very close contact with the inside wall of said magnetic core and also into close contact with each other as depicted in FIG. 7C. The ratio D /D of the outside diameter to the inside diameter and the ratio L/D of the length to the inside diameter of the above mentioned magnetic core are properly selected in winding the wires.

FIG. 8 shows insertion losses against the ratios D /D at frequencies of 40 to 250 mc./s. in an impedance transformer according to the present invention wherein the primary winding and secondary winding are wound by two turns and one turn, respectively, and are connected in a balanced to unbalanced on a cylindrical magnetic core of an outside diameter of mm., ratio D /D of the outside diameter to the inside diameter varied to be 2.5, 3.3 and 5 length of 20 mm.

FIG. 9 shows insertion losses against the ratios L/D at frequencies of 40' to 250 mc./s. in an impedance transformer wherein the primary Winding and secondary winding are wound by two turns and one turn, respectively, and are connected in a balanced to unbalanced on a cylindrical magnetic core of an outside diameter of 5 mm., inside diameter of 1 mm. and ratio L/D of the length to the inside diameter varied to be 10, and 20.

As evident from FIGS. 8 and 9, the larger the ratio D /D of the outside diameter to the inside diameter of the cylindrical magnetic core, the smaller the insertion losses at the respective frequencies and also the larger the ratio L/ D of the length to the inside diameter, the smaller the insertion losses and the better the high frequency transmitting characteristics.

Therefore, in the present invention, the cylindrical magnetic core is formed of a magnetic body for high frequencies, the ratio of the outside diameter to the inside diameter and the ratio of the length to the inside diameter of the magnetic core are selected to be more than 5 and more than 10, respectively, so that the insertion oss may be less than 3 db.

FIG. 10 shows an example of application of an impedance transformer according to the present invention as used as a transformer for the impedance matching of the input circuits of a television receiver of an antenna circuit of 3009 and an input circuit of 759.

As described above, according to the present invention, only by limiting the shape and dimensions of an impedance transformer, the impedances of the antenna circuit and input circuit can be matched with each other, the high frequency transmitting characteristics can be improved and the transformer can be made smaller.

What is claimed is:

1. An impedance transformer comprising a high frequency magnetic core having a single close-in type through hole, and a primary winding thereon wound by at least two turns and a secondary winding thereon wound by one turn, both of Said windings being maintained in close contact with the inside wall of said hole of the core, the respective turns of said primary and secondary windings in regions inside said hole being brought into close contact with one another, and the respective turns of said primary winding in regions outside said hole being spaced from each other as far as possible.

2. An impedance transformer comprising a high frequency cylindrical magnetic core having a single close-in type through hole, and a primary winding thereon wound by at least two turns and a secondary winding thereon wound by one turn, both of said windings being maintained in close contact with the inside wall of said hole of the core, the respective turns of said primary and secondary windings in regions inside said hole being brought into close contact with one another, the respective turns of said primary winding in regions outside said hole being spaced from each other, the ratio of the outside diameter to the inside diameter of said core being more than 5, and the ratio of the length to the inside diameter of the core being more than 10.

References Cited UNITED STATES PATENTS 1,748,857 2/1930 Wellings et al. 336- XR 2,594,890 4/1952 Ellwood 336-475 XR 2,826,747 3/1958 Carey 336229 XR 3,195,076 7/1965 Morrison 336-221 X'R 3,230,488 1/1966 Jacob 336-229 XR 3,327,220 6/1967 Podell 33325 XR LEWIS H. MYERS, Primary Examiner.

T. J. KOZMA, Assistant Examiner.

US. Cl. X.R. 

